Dividing the Water

Dividing the Water

Many physical signs of unsustainable water use authenticate the numerical indicator of water stress. Perhaps most important, evidence suggests that the amount of freshwater that can sustainably be supplied to farmers is nearing its limit. Groundwater overpumping and aquifer depletion are now occurring in many of the world’s most important crop-producing regions-including the western United States and large portions of India, as well as parts of north China, where water tables are dropping 1 meter a year. This signals not only that limits to groundwater use have been exceeded in many areas, but also that a portion of the world’s food supply is produced through unsustainable water use.

Like groundwater, many of the planet’s major rivers are suffering from overexploitation. In Asia, where the majority of world population growth and additional food needs will be centered in the years ahead, many rivers are completely tapped out during the drier part of the year, when irrigation is essential. These include most rivers in India-among them the mighty Ganges, a principal water source for densely populated and rapidly growing South Asia, and China’s Yellow River, whose lower reaches ran dry for an average of 70 days a year in each of the last 10 years and for 122 days in 1995. Demand for water is exceeding the Yellow River’s capacity to supply it.

Crop production may be even harder hit in these and other areas as population growth and urbanization push up water demands. Worldwide, the number of urban dwellers is expected to double to 5 billion by 2025. With political power and money concentrated in the cities, and with insufficient water to meet all demands, governments will face strong pressures to shift water out of agriculture even as food demands are rising. In fact, the reallocation of water from farms to cities is well under way in both industrial and developing countries. In California, for instance, a 1957 water plan projected that 8 million hectares of irrigated land would ultimately be developed statewide, yet the state’s irrigated area peaked in 1981 at 3.9 million hectares, less than half this amount. Net irrigated area fell by more than 121,000 hectares during the 1980s. California officials project an additional net decline of nearly 162,000 hectares between 1990 and 2020, with most of the loss owing to urbanization as the population expands from 30 million to a projected 49 million.

In China, water supplies are being siphoned away from farmlands surrounding Beijing to meet that city’s rising domestic, industrial, and tourist demands. The capital’s water use now exceeds the capacity of its two main reservoirs, and farmers in the agricultural belt that rings the city have been cut off from traditional sources of irrigation water. With some 300 Chinese cities now experiencing water shortages, this shift is bound to accelerate.

Similarly, growing demand in the megacities of Southeast Asia-including Bangkok, Manila, and Jakarta-is already partially met by overpumping groundwater. With limited new sources to tap, pressures to shift water out of agriculture will mount in these regions as well.

Unfortunately, no one has tallied the potential effect on future food production of the progressive shift of water from agriculture to cities combined with groundwater overpumping, aquifer depletion, and the other forms of unsustainable water use. Without such assessments, countries have no clear idea how secure their agricultural foundations are, no ability to accurately predict their future food import requirements, and no sense of how or when to prepare for the economic and social disruption that may ensue as farmers lose their water.